Tissue Engineering. Tissue engineering may be defined as the art of reconstructing or regenerating mammalian tissues, both structurally and functionally (Hunziker, Osteoarth. Cart. 10: 432-63, 2002). Tissue engineering generally includes the delivery of a synthetic or natural scaffold that serves as an architectural support onto which cells may attach, proliferate, and synthesize new tissue to repair a wound or defect.
An example of a tissue that is prone to damage by disease and trauma is the articular cartilage, one of several types of cartilage in the body, found at the articular surfaces of bones. Damage to cartilage may result from an inflammatory disease such as rheumatoid arthritis, from a degenerative process such as osteoarthritis or from trauma such as intraarticular fracture or following ligament injuries. Cartilage lesions are often associated with pain and reduced function, generally do not heal and without medical intervention may require total joint replacement.
Current therapeutic strategies for repairing damaged cartilage encompass procedures that induce a spontaneous repair response and those which reconstruct the tissue in a structural and functional manner. The former includes surgical techniques that expose the subchondral bone thereby allowing the infiltration of bone marrow progenitor cells to initiate the healing response. Often the induced tissue is of a mixed fibrocartilage type, is not durable and the clinical improvements are short lived. The latter strategy includes transplantation of chondral or osteochondral cells or tissue from either an autologous or an allogeneic source. Autologous Chondrocyte Transplantation (ACT) relies on transplanting into a cartilage lesion autologous chondrocytes, which have been isolated from a patient's cartilage biopsy and expanded in vitro. In fact, this technique requires a complicated procedure involving two surgical sites, and shows high variability and limited clinical success.
Matrices useful for tissue regeneration and/or as biocompatible surfaces useful for tissue culture are well known in the art. These matrices may therefore be considered as substrates for cell growth either in vitro or in vivo. Suitable matrices for tissue growth and/or regeneration include both biodegradable and biostable entities. Among the many candidates that may serve as useful matrices claimed to support tissue growth or regeneration are gels, foams, sheets, and porous structures of different forms and shapes.
Porous materials formed from synthetic and/or naturally occurring biodegradable materials have been used in the past as wound dressings or implants. A porous material provides structural support and a framework for cellular in-growth and tissue regeneration. Preferably, the porous material gradually degrades and is absorbed as the tissue regenerates. Typical bioabsorbable materials for use in the fabrication of porous wound dressings or implants include both synthetic polymers and biopolymers such as structural proteins and polysaccharides. The biopolymers may be either selected or manipulated in ways that affect their physico-chemical properties to provide greater or lesser degrees of flexibility or susceptibility to degradation.
Many natural polymers have been disclosed to be useful for tissue engineering or culture, including various constituents of the extracellular matrix including fibronectin, various types of collagen, and laminin, as well as keratin, fibrin and fibrinogen, hyaluronic acid, heparan sulfate, chondroitin sulfate and others. U.S. Pat. Nos. 6,425,918 and 6,334,968 disclose a freeze-dried bioresorbable polysaccharide sponge and use thereof as a matrix or scaffold for implantation into a patient.
Fibrin. Fibrinogen is a major plasma protein, which participates in the blood coagulation process. Upon blood vessel injury, fibrinogen is converted to insoluble fibrin which serves as the scaffold for a clot. Blood coagulation of is a complex process comprising the sequential interaction of a number of plasma proteins, in particular of fibrinogen (factor 1), prothrombin (factor II), factor V and factors VII-XIII. Other plasma proteins such as Von Willebrand factor, immunoglobulins, coagulation factors and complement components also play a part in the formation of blood clots.
Fibrin is known in the art as a tissue adhesive medical device useful for wound healing and tissue repair. Lyophilized plasma-derived protein concentrate (comprising fibrinogen, Factor XIII and fibronectin), in the presence of thrombin and calcium ions forms an injectable biological sealant (fibrin glue). U.S. Pat. No. 5,411,885 discloses a method of embedding and culturing tissue employing fibrin glue.
U.S. Pat. No. 4,642,120 discloses the use of fibrinogen-containing glue in combination with autologous mesenchymal or chondrocytic cells to promote repair of cartilage and bone defects. U.S. Pat. No. 5,260,420 discloses a method for preparation and use of biological glue comprising plasma proteins for therapeutic use. U.S. Pat. No. 6,440,427 provides an adhesive composition consisting substantially of fibrin forming components and a viscosity enhancing polysaccharide such as hyaluronic acid. A freeze-dried fibrin clot for the slow release of an antibiotic is described by Itokazu (Itokazu et al., Infection 25:359-63, 1997).
U.S. Pat. No. 5,972,385 discloses a lyophilized crosslinked collagen-polysaccharide matrix, with optional fibrin, that is administered per se or in combination with therapeutics for tissue repair. U.S. Pat. Nos. 5,206,023 and 5,368,858 disclose a method and composition for inducing cartilage repair comprising dressing the site with a biodegradable matrix formed by mixing matrix forming material with a proliferative agent and a transforming factor.
A fibrinogen-containing freeze-dried fleece-like structure for use as a wound dressing, filling for bone cavities or support material for release of active materials has been disclosed in U.S. Pat. No. 4,442,655. The structure is prepared by premixing fibrinogen and thrombin solutions, pouring into a mold, freezing and lyophilizing.
A freeze-dried fibrin web for wound healing has been disclosed in U.S. Pat. Nos. 6,310,267 and 6,486,377. The preparation of said web necessitates a single- or multi-stage dialysis of the fibrinogen solution. According to that disclosure, the single-stage or multistage dialysis of the fibrinogen solution changes crucially its composition by reducing the concentration of salts and amino acids. The dialysis is carried out in an aqueous solution of a physiologically compatible inorganic salt and an organic complexing agent.
A storage stable fibrin sponge containing a blood clotting activator for hemostasis, tissue adhesion, wound healing and cell culture support is disclosed in WO 99/15209. According to that disclosure, the restoration of moisture or water content following lyophilization is crucial for obtaining a soft, adaptable, absorbent sponge. The sponge may be impregnated with additives such as a blood clotting activator, stabilizers, preservatives and other agents.
U.S. Pat. Nos. 5,466,462 and 5,700,476 disclose a bioresorbable heteromorphic sponge comprising a biopolymer matrix structure, at least one substructure and at least one pharmacologically active agent. The substructures allow the incorporation of one or more active agents into the final product for physic release. U.S. Pat. No. 5,443,950 relates to the growth of cells derived from a desired tissue on a pre-established stromal support matrix. U.S. Pat. No. 5,842,477 discloses a method of in vivo cartilage repair by implanting a biocompatible, three-dimensional scaffold in combination with periosteal/perichondrial tissue and stromal cells, with or without bioactive agents.
Fibrinolysis
Existing freeze-dried fibrin implants for tissue engineering purposes are prepared using fibrinogen or plasma protein solutions having inherent proteases that may compromise the stability of certain of the plasma proteins and lead to degradation of the matrix. Plasminogen is a major plasma protein that binds fibrin during clot formation. Within the clot or matrix, plasminogen is enzymatically converted to plasmin, which functions as a fibrinolytic agent, resulting in the degradation of the clot or matrix. This process is typically retarded by the addition of anti-fibrinolytic agents, including but not limited to aprotinin, ε-aminocaproic acid or tranexamic acid into the composition. These agents may have detrimental effects on cell growth, proliferation and/or differentiation or may cause adverse reactions in patients. The art has not heretofore provided a stable freeze-dried fibrin matrix substantially devoid of exogenous anti-fibrinolytic agents.
Copending international patent application WO 03/007873 by some of the applicants of the present invention of the present invention, discloses a freeze-dried plasma protein matrix comprising plasma proteins and at least one anti-fibrinolytic agent, optionally comprising selected auxiliary agents to improve certain physical, mechanical and biological properties of the matrix.
Thus, there remains an unmet need for a fully biocompatible, true three-dimensional, plasma protein matrix, for in vitro and in vivo cell growth and tissue regeneration, substantially devoid of fibrinolytic activity and exogenous anti-fibrinolytic agents thus obviating the need for exogenous anti-fibrinolytic agents.